The invention relates to a target apparatus for positioning a drilling tool with respect to a drill channel to be created, consisting of a target hook and a guide arm releasably fastened to this, on which there is arranged a receiver for the drilling tool and on which there is formed a guide path in the form of a laterally through-going open groove for the guide arm which is displaceable and fixable in the guide path.
Such target apparatus are applied for reconstruction for example of a ligament in the knee joint which has torn for example on account of an accident. In particular, for the replacement of the front cruciate ligament with the quadriceps tendon by way of an arthroscopic operation there exists the possibility of an implant-free anchorage of a part of the quadriceps tendon. Within the framework of this operation it is required to obtain a spongy bone cylinder from the tibia with which the defect filling at the patella and the additional transplant blockage in the tibia may be carried out. For this a drill channel must firstly be placed in the tibia and the femur in an exact manner.
For an exact as possible placing of drill channels one uses target apparatus of the previously mentioned type. Such a target apparatus is known from U.S. Pat. No. 5,968,050. This comprises a guide arm on which the drilling tool may be attached via a suitable receiver. For aligning the drilling tool a target hook is connected to the guide arm, which may be aligned at a previously set angle to the guide arm. The target hook at its distal region has an arcuate shape with a sharp tip which serves for anchoring the end of the target hook on the bone during the drilling procedure, so that the target apparatus may not slip away. Similar designs are known from U.S. Pat. Nos. 4,672,957, 5,154,720 and 5,350, 383 and from EP 0 797 955 A1.
A disadvantage of these target apparatus lies in the fact that the arcuate target hook to be introduced into the joint cavity may create injuries on account of the sharp tip. Although this risk may be kept small with the correct handling of the apparatus and with a careful execution of the endoscopic operation, it may never be completely ruled out.
On account of the arcuate shape of the target hook there further arises the disadvantage that an exact positioning of the bore to be incorporated into the bone is not possible on account of the constantly present mismatch between the tip of the target hook and the through bore for the required guide wire and the drill, which is located at a distance to this tip.
Finally with known target apparatus it is also disadvantageous that on account of design and an account of the anatomical conditions, after an effected incorporation of the bore it is very difficult to be able to be removed again out of the cavity of the joint, not least because a prior separation of the guide arm from the target hook is not possible due to the restricted space conditions. There therefore exists the danger that injuries may occur also in this phase of the operation.